age = input("please input your age:")
print(type(age))

if int(age) >= 30:  # 如果用age会报类型错误。python3中input默认接收的都是字符串，需要用int强转
    print("you must good good study!")
elif int(age) < 10:  # 注意 else if要简写成elif。4个字母。否则会报错
    print("you are a baby")
else:
    print("you are young!");

height = 1.64  # m
weight = 55.0  # kg
BMI = weight / (height * height)
print(BMI)
if BMI < 18.5:
    print("体重太轻了")
elif BMI >= 18.5 and BMI <= 25:
    print("体重正常")
elif BMI > 25 and BMI <= 28:
    print("过重")
elif BMI > 28 and BMI <= 32:
    print("肥胖")
elif BMI > 32:
    print("严重肥胖")
